1. Field of the Invention
The present invention relates to a vibration generating element and a vibration driven motor or actuator for relatively driving a movable member urged against a vibrating member by a vibration generated in the vibrating member, in which the vibrating member vibrates upon reception of the vibration from the vibration generating element. More particularly, the present invention relates to a structure around a frictional sliding portion of the movable member.
2. Related Background Art
A vibration driven motor or actuator, includes a vibrating member formed into a bar or pencil shape, and a movable member urged against the driving surface of the vibrating member, which members are coaxially arranged. Upon synthesis of bending vibrations excited upon application of AC voltages to piezoelectric elements of the vibrating member, a circular or elliptic motion is generated in surface grains of the driving surface of the vibrating member, thereby frictionally driving the movable member.
FIG. 6 is a schematic sectional view of a conventional bar-shaped vibration driven motor. In FIG. 6, the motor includes a vibrating member 1, which clamps and fixes driving piezoelectric elements 8, and the like between vibrating member structural bodies 1a and 1b, and a movable member 2 urged against the driving surface of the vibrating member structural body 1a by a spring means (not shown).
Anodized aluminum is used as a frictional sliding material of the frictional sliding surface of the movable member, and the entire frictional sliding surface contacts the frictional driving surface of the vibrating member.
In the prior art, when the motor is driven, at least one edge of the frictional or contact sliding surface of the movable member strongly contacts the frictional driving surface of the vibrating member. A for the following reason. That is, a contact sliding portion 2a of the movable member receives a force upon displacement of a contact sliding portion 1aa of the vibrating member. The direction of displacement of the vibrating member is not perpendicular to the contact surface but is included relative thereto. A flange-shaped spring structure of the contact sliding portion of the movable member is also deformed, so that the contact surface is inclined. Therefore, the frictional sliding surface 2a of the movable member contacts the frictional sliding surface 1aa of the vibrating member to form a certain angle therebetween.
More specifically, weak edges 2aa and 2ab of the frictional sliding surface 2a, formed of anodized aluminum as an inorganic material, of the movable member strongly contact the frictional sliding surface 1aa of the vibrating member.
Thus, the anodized-aluminum edges crack, and once the edges crack, the cracked state gradually gets worse. For this reason, the displacement of the vibrating member can no longer be smoothly transmitted to the movable member. As a result, the starting torque is considerably reduced, or the cracked anodized-aluminum powder serves as an abrasive, and the frictional driving portion of the movable member is immediately worn. In addition, an output from a sensor phase for detecting the vibrating state of the vibrating member 1 becomes unstable, and feedback control is disabled.